Base16 theme switcher for fish shell

1. If you have fisher,

$ fisher add tomyun/base16-fish

2. Run your choice of base16-* function

$ base16-oceanicnext

1. Why not just use base16-shell?

base16-shell is great for bash/zsh, but unable to support syntax highlighting colors in fish that ends up with incorrect coloring of texts typed in the prompt. base16-fish fixes this problem by explicitly setting color variables in native fish shell scripts. With that, no separate helper required in config.fish. No configuration file (.base16_theme) stored in your home directory. Theme switching commands (base16-*) are now fish functions that work more nicely with tab completetion.